Method of drilling wells



D. RAGLAND ET AL METHOD OF DRILLING WELLS Filed May 10, 1952 23 Flow Line FIG. 3.

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FIG. 2.

ted States Pat mo METHOD on DRILLING WELLS Douglas Ragland and George Edward Cannon, Houston, Tex., assignors, by mesne assignments, to Esso Research and Engineering Company, Elizabeth, N. J., a corporation of Delaware Application May 10, 1952, Serial No, 287,168

4 Claims, (Cl. 255--1.8)

The present invention is directed to a method of drilling a well in which a hollow drill stem having a drill bit attached to it is rotated. More particularly, the invention is concerned with a method for drilling a well in which the weight of the drilling mud is decreased to avoid loss of mud in highly permeable formations. In its more specific aspects the invention is directed to a drilling operation in which mud is circulated which involves the reduction of the weight of the mud during the circulation.

The present invention may be briefly described as a method of drilling a well, particularly an oil well, in which a hollow drill stem having a drill bit attached to a lower end thereof and in which a drilling fluid is circulated down the drill stem and through a passageway in the drill bit and then up an annulus between the drill stem and a wall of the well bore. The particular feature of the present invention is incorporating in the drilling fluid as it circulates in a well a weight reducing amount of a gasiform fluid to prevent the loss of drilling fluid below a preselected value to highly permeable formations penetrated by said drill bit. While the drilling operation is conducted in such highly permeable formations, the drilling fluid is continuously circulated and there is continuously incorporated therein the gasiform fluid. Thereafter when the highly permeable formation has been passed and when the loss of drilling fluid to formations penetrated by said bit is below the preselected value, the incorporation of gasi'form fluid into the drilling fluid is discontinued to increase the weight of the drilling fluid to a mud or drilling fluid having a normal weight for the particular depth and conditions employed.

The gasiform fluid employed in the practice of our invention may be air or natural gas or any other suitable gasiform fluid. It may be desirable in some instances to use inert gases, such as nitrogen, methane, ethane, propane, and the like, or mixtures thereof.

The gasiform fluid may be introduced into the circulating mud at the surface of the well and particularly into the stand pipe by a suitable connection thereto following which the aerated or gasified mud is then pumped down the hollow drill stern through the eyes of the bit and then up the annulus. The gasiform fluid preferably may be introduced into the annulus at a predetermined depth below the surface of the well. This may suitably be done by having at least a small conduit or conduits tap the casing at a pre-selected depth and air or gas injected into the annulus as the mud stream or the stream of drilling fluid proceeds up the annulus.

The present invention will be further illustrated by reference to the drawing in which Fig. 1 illustrates apparatus for carrying out a preferred mode of the invention;

Fig. 2 illustrates a detail of the attachment to the well casing; and,

Fig. 3 shows the arrangement for introducing gasiform fluid to the conduits of Figs. 1 and 2.

Referring now to the drawing, numeral 11 designates a well casing which is cemented in a well bore 12 to which is attached at predetermined levels small conduits 13 and 14 which are led to the earths surface through the cement 15 sheathing the casing 11 and connected to a manifold 16 which, in turn, is connected to a compressor, not shown. It is desirable that conduit 13 be larger than conduit 14 to compensate for pressure drop through the conduits and yet effectuate the beneficial aspects of the invention. Conduits 13 and 14 are provided, respectively, with valves 17 and 18 for control of flow of the gasiform fluid to the interior of casing 11 The casing 11 is provided with blow-out preventers 19 and 20 and a master valve 21 as is conventional practice. Attached to the well head assembly 22 is a iow line 23 for dis charge of drilling fluid from the annulus. The Well head assembly 22 is provided with a pressure drilling head 24 such as the Guiberson type El as illustrated in the Composite Catalogue of Oil Field and Pipeline Equipment, volume 1, page 2057, 1951 edition. Arranged in the well head and extending down the casing 11 is a hollow drill stem 25 down which the drilling mud is circulated. The drill stem 25 has a drill bit, not shown, attached to the lower end thereof.

Referring now to Fig. 2 which is an enlarged view of the connections of the conduits 13 and 14 to the casing 11 the conduit 13 or 14, as the case may be, is tapped into the casing 11 and may be welded thereto by suitable welds or other connections 26. The discharge end of the conduits 13 and 14 may suitably be provided with a suitable frangible disc, such as rupture disc 27, to prevent plugging of the conduits 13 and 14 during the cementing operation.

In the practice of our invention, it will be desirable to connect the conduits 13 and 14 to the casing 11 prior to the time when the casing is run into the hole and then allow it to be cemented therein during the cementing operation. It may be desirable when practicing the present invention employing this mode where the gasiform medium is introduced into the annulus to have the top 300 to 500 feet of the hole drilled to a diameter approximately 4 inches greater than current practice in order to maintain the proper clearance in the hole. In practicing the invention, drilling fluid, such as a suspension of clay or other finely divided materials and water, is circulated down the drill stem 25 and through the eyes of a bit, not shown, and up the annulus between the drill stem 25 and the interior of casing 11, the mud flowing outwardly to the mud pit through flow line 23. When it is indicated that mud returns are being lost above about 10%, the practice of our invention allows the weight of the drilling fluid to be reduced to prevent loss of returns. By starting up the compressor, not shown, which is attached to conduit 16, it is possible to introduce air or gasiform fluid through either or both of conduits 13 or 14 by suitable manipulation of valves 17 and 18. In this example of our invention the conduit 14 may be attached to the casing 11 at approximately 210 feet below the flow line 23 while the conduit 13 may be attached to the casing 11 at approximately 312 feet. In this operation the effective mud weight may be reduced at a depth of 5600 feet from 9.2 to 8.9 pounds per gallon while circulating mud at a rate of about 500 gallons per minute. Air may be supplied to the casing 11 at about 315 cubic feet per minute at a Working pressure of about pounds per square inch gauge on the compressor. At the beginning of the operations of reducing the mud weight air may be first injected through conduit 14 by opening valve 18, and thus rupturing disc 27, until an equilibrium point is reached. At this time the hydrostatic head at the lower point in the casing where the conduit 13 connects to the casing 11 would be reduced slightly less than 100 pounds and air would then be injected in the casing 11 through conduit 13 by opening valve 17 and closing valve 18, disc 27 in conia'tented Dec. 6, 1955 duit 13 being ruptured. Since the weight of the column of drilling fluid in the annulus has been reduced by incorporating air into the mud therein through conduit 14, it is then possible to inject air at a lower point in the casing 11 by conduit 13. Thus the air pressure available from the compressor, not shown,'has only to overcome the hydrostatic head of the column of drilling fluid in the annulus whose weight has been reduced. A plurality of conduits vertically spaced on the casing 11 may suitably be used to accomplish the beneficial results of our invention. Injection of'air would be continued into the casing 11 as long as drilling operations were conducted in the highly permeable formation where mud heretofore was lost to a great extent. tion has been passed or traversed by the drill bit, the weight of the mud may then be increased by closing off valve 16. In making a connection to the drill stem the air may be shut as and drilling operations resumed after the connection is made.

It is intended that our invention is not to be limited to the preferred mode. As mentioned before, air may be injected into the stand pipe and the mud, containing injected air, forced down through the drill stem and up the annulus, pressure being released when the mud is flowed into the mud ditch and mud pits.

It is also possible to practice our invention by suitably emulsifying the mud with a gasiform fluid, such as air, by providing a suitable mixing device, such as a jet or an impeller-type mud mixer to whip the mud up into a creamy mass containing air or other gasiform fluid. However, it is preferred to introduce the air or gasiform fluid into the annulus at a pre-determined point below the earths surface as has been described with respect to the drawing.

The nature and objects of the present invention having been completely described and illustrated, what we wish to claim as new and useful and to secure by Letters Patent is:

After the highly permeable forma- 1. A method of drilling a well under pressure by rotating a hollow drill stem having a drill bit attached to a lower end thereof which comprises the steps of pumping a drilling mud containing a suspension of finely divided fluids and having a normal weight for the particular depth of the well down the drill stern and through a passageway in the drill bit and up the annulus between the drill stem and a casing lining the wall of the well, injecting into the pumped drilling mud in said annulus at predetermined depths below the earths surface at a plurality of vertically spaced apart points a weight reducing amount of a gasiform fluid to prevent the loss of drilling mud above a preselected value about 10% by volume of the mud circulating in the well to formations penetrated by said drill bit, continuously pumping drilling mud and injecting gasiform fluid into the pumped drilling mud in said annulus, and then discontinuing said injection of gasiform fluid into said pumped drilling mud to increase its weight when the loss of drilling mud to formations penetrated by said bit is below said preselected value.

2. A method in accordance with claim 1 in which the gasiform fluid is air.

3. A method in accordance with claim 1 in which the gasiform fluid is natural gas.

4. A method in accordance with claim 1 in which the vertically spaced apart points are approximately 210 and approximately 312 feet below the earths surface.

References Cited in the file of this patent Germany June 20, 1933 

1. A METHOD OF DRILLING A WELL UNDER PRESSURE BY ROTATING A HOLLOW DRILL STEM HAVING A DRILL BIT ATTACHED TO A LOWER END THEREOF WHICH COMPRISES THE STEPS OF PUMPING A DRILLING MUD CONTAINING A SUSPENSION OF FINELY DIVIDED FLUIDS AND HAVING A NORMAL WEIGHT FOR THE PARTICULAR DEPTH OF THE WELL DOWN THE DRILL STEM AND THROUGH A PASSAGEWAY IN THE DRILL BIT AND UP THE ANNULUS BETWEEN THE DRILL STEM AND A CASING LINING THE WALL OF THE WELL, INJECTING INTO THE PUMPED DRILLING MUD IN SAID ANNULUS AT PREDETERMINED DEPTHS BELOW THE EARTH''S SURFACE AT A PLURALITY OF VERTICALLY SPACAED APART POINTS A WEIGHT REDUCING AMOUNT OF A GASIFORM FLUID TO PREVENT THE LOSS OF DRILLING MUD ABOVE A PRESELECTED VALUE ABOUT 10% BY VOLUME OF THE MUD CIRCULATING IN THE WELL TO FORMATIONS PENETRATED BY SAID DRILL BIT, CONTINUOUSLY PUMPING DRILLING MUD AND INJECTING GASIFORM FLUID INTO THE PUMPED DRILLING MUD IN SAID ANNULUS, AND THEN DISCONTINUING SAID INJECTION OF GASIFORM FLUID INTO SAID PUMPED DRILLING MUD TO INCREASE ITS WEIGHT WHEN THE LOSS OF DRILLING MUD TO FORMATIONS PENETRATED BY SAID BIT IS BELOW SAID PRESELECTED VALUE. 